[12:52:59 FATAL]: Error executing task
java.util.concurrent.ExecutionException: java.lang.AssertionError: TRAP
        at java.util.concurrent.FutureTask.report(FutureTask.java:122) ~[?:1.8.0_312]
        at java.util.concurrent.FutureTask.get(FutureTask.java:192) ~[?:1.8.0_312]
        at net.minecraft.server.v1_12_R1.SystemUtils.a(SourceFile:47) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.MinecraftServer.D(MinecraftServer.java:850) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.DedicatedServer.D(DedicatedServer.java:423) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.MinecraftServer.C(MinecraftServer.java:774) ~[patched_1.12.2.jar:git-Paper-1618]
        at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:666) ~[patched_1.12.2.jar:git-Paper-1618]
        at java.lang.Thread.run(Thread.java:748) [?:1.8.0_312]